The following samples were shot with a Canon EOS 7D
using 10x Live View MF and RAW image format.
The RAW files were set to the Standard Picture Style with sharpness set to "2" (low) and processed into 16-bit TIFF files in DPP.
The web-ready images were produced by Photoshop CS4's Save-for-Web at a 70 quality setting.

Focal lengths are approximate, so use good judgment when evaluating details that may be larger in one lens' test image than another's.
Also, because of the time required to test so many lenses at so many settings, the sun moves during the test.
When the sun moves, so do the shadows.
So, I alert you to the need to look past the position of the shadows to see the real differences between the lenses.

The selected crops (the Whitespire tree clump, the roof and branches, the rock and the flowers) are in line with the plane of sharp focus.
Any curvature of field would of course cause these parts of the images to be more blurred.
Many of the images show foreground and/or background that could help with this determination -
I didn't see anything substantially different in the full-size pics.
I personally prefer no curvature of field.

The center of the image is nearly always the sharpest and that is the case with the lenses compared here.
Actually, they all perform nicely in the center.
Quite often the subject of a photo will be 1/3 of the way into the frame,
so I selected objects off-center but in the plane of sharp focus that showed the more substantial differences between the tested lenses.

Please be patient - there are about 13MB of images required to load the comparisons below.
When they are loaded, the mouseclick bars will function properly.

Image detail size changes an especially large amount in the first set of comparisons below as these images are from
the widest available focal length (15-18mm) on each lens.
These sample crops were taken from a location about 33% into the left side of frame.

The EF-S 17-55 is the best performer in this comparison, showing the least CA (this is a monochrome tree) and best sharpness.
The EF-S 15-85 is not far behind it and clearly better than the rest of these lenses including the EF-S 17-85.

The 24mm sample crops below were taken from a location about 25% into the left side of the frame.

In this 24mm sample, the EF-S 15-85 and the EF-S 17-55 perform very similarly and noticeably better than the rest of this field.
The EF-S 18-55mm IS kit lens performs the worst at this focal length/frame position with the balance of the lenses performing similarly in the middle.

The 35mm sample crops below were taken from a location about 20% into the top/left of the frame.

Again in this sample at 35mm, the EF-S 15-85 and the EF-S 17-55 perform similarly and noticeably better than the rest of this field.
The EF-S 18-55mm IS kit lens performs better at this focal length/frame position - more similarly to the rest of the balance of the lenses.

The 50mm sample crops below were taken from a location about 15% into the right side of the frame.

I think the EF-S 15-85 looks slightly better than even the EF-S 17-55 at this focal length.
- and the inexpensive EF-S 18-135 is looking impressive at this position in the frame.
The 17-55 is at its max focal length in this example (55mm) - as is the EF-S 18-55 where it is at its weakest.
The EF-S 18-200 performs nicely at f/8 in this example.
Another note is that the EF-S 17-85 performs better on the left side of the frame at this and the next-compared focal lengths.

The 70mm sample crops below were taken from a location about 33% into the right side of the frame.

With the EF-S 17-55 out of the competition, the EF-S 15-85 gets the win at the wide open aperture
The EF-S 18-135 competes very well at this position in the frame at f/8.
Again, remember to account for the changing sun angle when making comparisons - the harder angle of the sun in the EF-S 18-135mm sample gives it an advantage.
The EF-S 18-200 is not competing in this round - Sorry, I can't find the samples shots for this one.

The 85mm sample crops below were taken from a location about 25% into the right side of the frame.

I again give the EF-S 15-85 the win at 85mm at the wide open aperture but the EF-S 18-135 once again looks good at f/8 at this selected position in the frame.

Out of these selected lenses, the
Canon EF-S 17-55mm f/2.8 IS USM Lens and
Canon EF-S 15-85mm f/3.5-5.6 IS USM Lens
produce the best image quality.
Perhaps most surprising to me was how good the
Canon EF-S 18-135mm f/3.5-5.6 IS Lens looks at f/8 at the longer focal lengths in this comparison.
While I included this lens in the original testing group, the inclusion of the EF-S 18-135mm results on this page happened after the EF-S 15-85mm review was published.
The areas selected for the longer focal length crops happened to be in a sweet spot for this lens.
Overall, I would rate the EF-S 18-135 closer to the EF-S 18-200mm for image quality.